Sorry Sir Richard, there is no such thing as sustainable aviation fuel

Sir Richard Branson crossed the Atlantic yesterday in a Virgin Dreamliner powered almost entirely by ethanol and used cooking oil.

So what? It was the first time a commercial airliner had completed a long-haul flight with 100 per cent “alternative” fuel in its tanks. It was also close to 100 per cent greenwash. The airline industry calls this kerosene substitute sustainable aviation fuel (SAF), but except for the purposes of lobbying and political slogans there is no such thing.

Not SAF at any speed. SAF is a refined blend of waste oils, animal fats and ethanol from corn. It currently accounts for 0.1 per cent of fuel burned by airliners. At least 30 airlines say they want to boost that to 10 per cent by 2030, and the Biden administration wants to increase US production nearly 200-fold in the same timeframe.

That would be a problem.

• Emissions. SAF is a hydrocarbon, just like normal jet fuel, and it emits the same amount of CO2 when burned. Yesterday’s flight burned 70 tonnes of it, producing 220 tonnes of CO2.
• Feedstock. The difference is that SAF’s feedstock (plants and livestock) absorbed carbon from the atmosphere recently whereas kerosene’s feedstock (oil) did so millions of years ago. 
• Land use. SAF’s promoters say it cuts emissions by 70 per cent relative to jet fuel because its feedstock is renewable. That takes no account of methane emissions from livestock, unsustainable land use for ethanol, or the fact that SAF creates carbon emissions that could have been avoided if the waste oils were simply disposed of responsibly. A recent report by the Royal Society found that meeting the UK’s entire aviation fuel needs with “energy crops” would take more than half the country’s farmland.
• Production. SAF requires an expensive, energy-intensive three-stage refining process that currently produces fuel at roughly four times the cost of kerosene, although the industry hopes economies of scale will bring that down.
• Perception. SAF may persuade credulous travellers flying is green. It isn’t. If concerned, they would do better to fly less, and the industry should invest heavily in separate carbon removal technologies such as direct air capture. 

Does real SAF exist? Yes. This just isn’t it. Real sustainable aviation fuel would have to be pure green hydrogen fed into adapted engines, or green hydrogen combined with CO2 obtained from carbon capture. But weight for weight, green hydrogen currently costs roughly ten times as much as kerosene.

So why bother? From Virgin’s point of view the point of yesterday’s flight was to raise public awareness of SAF as a concept and demonstrate regulatory progress in the form of its permit to fly. The usual limit for SAF mixed with normal jet fuel is 50 per cent. 

For the broader aviation industry the focus on SAF serves three purposes:

• to introduce the concept of sustainable aviation fuel into public discourse even though saying it’s sustainable doesn’t make it so;
• to start making a case for the very large subsidies that would be needed to make SAF economic for airlines; and
• to shift attention away from very large subsidies they already receive relative to ground transport because jet fuel isn’t taxed.

“Airlines want to argue that because alternative fuels are made from waste plant matter, this offsets the emissions from the flight. But that’s misleading,” says Cait Hewitt of the Aviation Environment Federation, an NGO. “Turning it into aircraft fuel means putting more CO2 in the air today.”

There’s another option, being tried by American Airlines: collect carbon credits by buying up sawdust, compressing it into bricks, wrapping them so they won’t leak carbon, and burying them.